1. Field of the Invention
The present invention relates to a blood-pressure determining apparatus which determines a blood pressure of a portion of a living subject; such as a brachial portion or a cervical portion of the subject.
2. Related Art Statement
When a disease of a central artery of a living subject, such as coronary artery or aorta ascendens, is inspected, it is desirable to measure a blood pressure of a central portion of the subject. However, it is not easy to measure a blood pressure of a more central portion than a brachial portion. For example, it is difficult to accurately measure a blood pressure of a cervical portion, i.e., a carotid-artery blood pressure, even in an invasive method. Thus, it has been practiced to measure a blood pressure of a brachial portion also when a disease of a central artery such as coronary artery or aorta ascendens, is inspected.
Meanwhile, it is known that when blood pressure values of a living subject who is taking a face-up position are measured, diastolic and mean blood pressure of a carotid artery of the subject (hereinafter, referred to as cervical diastolic and mean blood pressure CBP(DIA), CBP(MEAN), respectively) are substantially equal to diastolic and mean blood pressure of a brachial portion of the subject (hereinafter, referred to as brachial diastolic and mean blood pressure BBP(DIA), BBP(MEAN), respectively), respectively, but a systolic blood pressure of the carotid artery (hereinafter, referred to as cervical systolic blood pressure CBP(SYS)) is not equal to a systolic blood pressure of the brachial portion (hereinafter, referred to as brachial systolic blood pressure BBP(SYS)).
A carotid-pulse-wave detecting device has recently been improved and can accurately detect a waveform of a carotid pulse wave, wc. However, an absolute blood pressure in a carotid artery cannot be accurately determined based on only the carotid pulse wave wc detected by the carotid-pulse-wave detecting device. Hence, it is considered to convert, based on a brachial blood pressure BBP measured using a cuff, a carotid pulse wave wc detected by the carotid-pulse-wave detecting device, into a cervical blood pressure CBP.
FIG. 1 shows a heartbeat-synchronous pulse of a carotid pulse wave wc detected by the carotid-pulse-wave detecting device. Since a minimum-magnitude, a, an area-gravity-center magnitude, b, and a maximum magnitude, c, of the heartbeat-synchronous pulse of the carotid pulse wave wc correspond to a cervical diastolic blood pressure CBP(DIA), a cervical mean blood pressure CBP(MEAN), and a cervical systolic blood pressure CBP(SYS), respectively, a relationship represented by the following Expression 1 is obtained:c−a:b−a=CBP(SYS)−CBP(DIA):CBP(MEAN)−CBP(DIA)  (Expression 1)
As described above, cervical diastolic and mean blood pressure CBP(DIA), CBP(MEAN) are substantially equal to brachial diastolic and mean blood pressure BBP(DIA), BBP(MEAN), respectively. Therefore, a cervical systolic blood pressure CBP(SYS) can be determined by replacing, in Expression 1, the cervical diastolic and mean blood pressure CBP(DIA), CBP(MEAN) with the brachial diastolic and mean blood pressure BBP(DIA), BBP(MEAN), respectively.
However, in each blood-pressure measuring operation using a cuff, an accurate brachial diastolic blood pressure BBP(DIA) is measured, but an accurate brachial mean blood pressure BBP(MEAN) may not be measured. Therefore, if a brachial mean blood pressure BBP(MEAN) measured using a cuff is used in place of a cervical mean blood pressure CBP(MEAN), the thus obtained cervical mean blood pressure CBP(MEAN) and a cervical systolic blood pressure CBP(SYS) calculated based on the cervical mean blood pressure CBP(MEAN) may not be sufficiently accurate.